1. Field of the Invention
This invention relates to a developing apparatus for making latent electrostatic images visible in an electrophotographic apparatus or electrostatic recording apparatus, and to an image forming apparatus capable of obtaining high-quality images using the developing apparatus.
2. Description of the Related Art
Conventionally, developing apparatus utilizing a single-component toner supplies developer to the surface of a developer bearing member (herein after also referred to as a toner carrier, developer roller, etc.) by an elastic roller of sponge or the like which rotates, electrically charges the developer and causes it to adhere, restricts the thickness of the developer layer by a blade or roller-shaped layer thickness regulating member, forms a uniform thin layer of developer on the surface of the developer bearing member, causes it to adhere to a latent electrostatic image formed on a latent image carrier, develops that, and turns it into a visible image.
At such time, there have been the following problems with the layer thickness regulating member.
Conventionally, for the surface member of the layer thickness regulating member, in view of the fact that the electrostatic charging characteristics of the developer are affected by the frictional electrostatic charging characteristics of the various members, when a negatively charged developer is used, a positively charged material has sometimes been used for the purpose of increasing the developer charge or conversely decreasing the oppositely charged developer.
In particular, because nylon materials exhibit very strong positive charging qualities, they have been frequently used for the purpose of improving the charging characteristics of developers. Examples include nylon and polyether copolymers (Japanese Patent Application Laid-Open No. H9-50185/1997), nylons having specific mechanical properties (Japanese Patent Application Laid-Open No. H8-328381/1996), and nylons formed on urethane rubber (Japanese Patent Application Laid-Open No. H8-248769/1996). Developer bearing members are generally classified in two types, hard and soft types according to the shape of the photo-sensitive member (drum or belt) and developing method (contact or non-contact), and layer thickness regulating member are needed which accord therewith.
However, nylon materials exhibit poor releasability, leading to problems such as that the developer strongly adheres to the surface of the layer thickness regulating member, so-called toner sticking occurs, the charging characteristics of the developer changes over time, and the phenomenon of streaks or irregularities occurring in the thin developer layer arises.
Also, when the coefficient of friction (xcexc) of the layer thickness regulating member is large, toner aggregates or foreign matter is sandwiched between parts of the layer thickness regulating member and developer roller that are in contact, and streaks occur in the thin toner layer, making it difficult to obtain a uniform stable thin layer.
Meanwhile, as a method of maintaining long life of a developing apparatus (hereinafter also referred to as a developing unit), as affected by toner sticking, developing apparatuses have been proposed (cf. Japanese Utility Model Application Laid-Open No. S63-364/1988 (published), for example) wherein, a thin layer roller driven to turn in the same direction as the developer roller by a drive source is made to contact the developer roller.
Here, the turning speed of the developer roller is set to a prescribed speed that satisfies the developing conditions, and the turning speed of the thin layer roller is set so that the thin layer roller turns at a very low speed.
In this developing apparatus, the thin layer roller that makes the toner adhering to the surface of the developer roller a thin layer contacts the developer roller at only one place, and the place where the thin layer roller contacts the developer roller (toner carrier) changes due to the turning of the thin layer roller, wherefore, as compared to the developer blade, it is difficult for toner sticking to occur on the thin layer roller, and useful life extension was expected.
However, in the above-described developing apparatuses wherein a thin layer roller is used, there was a problem, as described below, caused by toner aggregates that were generated inside the developing apparatuses.
That is, whereas the supply roller functioning as the toner supply member is generally made of a sponge material, when the sliding contact between the developer roller and the supply roller is repeated as the developing apparatus is used, portions of the sponge configuring the supply roller are torn away and circulate as minute foreign matter together with the toner inside the developing apparatus. When the developing apparatus is used over an extended period, toner adheres to the minute pieces of sponge torn away as described in the foregoing when toner is rubbed between the developer roller and the supply roller or between the developer roller and the thin layer roller, and toner fuses with toner at the site of that sliding contact, whereupon toner aggregates are generated.
These toner aggregates that are generated follow along the normal flow of toner and reach the vicinity of sliding contact between the developer roller and thin layer roller. The thin layer roller turns in the same direction as the developer roller, and renders the toner adhering to the surface of the developer roller into a thin layer. However, the turning speed of the developer roller is set at a prescribed speed which satisfies the developing conditions, whereas the turning speed of the thin layer roller is set so that the thin layer roller turns at a very low speed.
For that reason, toner aggregates that have gotten into the wedge-shaped portion at the entrance to the sliding contact region between the developer roller and the thin layer roller either are returned back to the interior of the developing apparatus without entering that sliding contact region, or enter into that sliding contact region. The toner aggregates that have entered the sliding contact region are used in the developing of the latent electrostatic images, causing anomalous images to be generated, or remain in the sliding contact region and adhere strongly to the surface of the thin layer roller, creating portions where no thin layer will be formed and causing white streaks in the images.
Furthermore, when the developing apparatus continues to be used with the toner aggregates present in the sliding contact region between the developer roller and the thin layer roller, the surfaces of the developer roller and thin layer roller where the toner aggregates make contact will deteriorate, and it will become impossible to obtain the desired thin toner film on the developer roller. For that reason, it is necessary to enhance the thin layer roller toner releasability, and prevent the aggregates from adhering to the thin layer roller surface.
In addition to the aggregates, moreover, toner also melts and adheres in a thin film form to the thin layer roller surface in what is called toner filming, and there has been hoped that thin layer roller surface toner releasability can be further improved.
As means for eliminating the difficulties described in the foregoing, the method of deploying a fluorine resin excelling in toner releasability to the thin layer roller surface is adopted. In addition to coating on the fluorine resin coating material by an ordinary method such as spraying or roll coating, this can be accomplished by mounting a fluorine resin tube to the thin layer roller surface.
However, although fluorine resins are very outstanding in terms of releasability and the difficulties noted earlier are eliminated, positioned, in triboelectric series, on the extreme negatively charged side, wherefore difficulties arise in that, especially when using a negatively charged toner, the toner charge amount is low, or, for that reason, a thin toner layer is not formed uniformly, or, when the fluorine content is decreased and the toner charging quality improved, toner releasability declines. Thus, even for the method in which a thin layer roller is employer, further improvement in toner releasability on the surface of the thin layer roller has been desired.
Furthermore, ordinarily, when developing a toner on a latent electrostatic image carrier, a broad division is made between developing methods wherein the developer roller and the latent electrostatic image carrier are not in contact and methods wherein they are in contact. As a general practice, the developer roller used is elastic or rigid, as necessary. Ordinarily, a rigid developer roller is often used in contact developing in which a belt-form latent electrostatic image carrier is used, or in non-contact developing.
At such time, in order to secure a suitable sliding contact portion between the thin layer roller and the developer roller, it becomes necessary to have a suitable degree of elasticity on the thin layer roller side. However, because toner releasability is poor when a rubber roller is used as is, a surface layer is generally provided to effect improvement, but when the flexibility is raised enough so that the elasticity of the rubber layer can be followed, releasability deteriorates, and the difficulties described earlier are encountered, constituting a problem.
Meanwhile, developer rollers also posed problems as described below. When a developer roller is used in, among those single-component developing schemes, a contact developing scheme wherein the developer roller and the photo-sensitive member are in a contacting condition.
With such a scheme, in order to cause the developer roller and the photo-sensitive member to stably contact each other, it is particularly necessary to impart flexibility to the structure or material of one or the other, or of both. For that reason, flexible materials and/or structures have been used, namely, an ending or endless belt for the photo-sensitive member, and rubber or sponge or the like for the developer roller.
However, in terms of apparatus cost, it is more economical to use a drum as the photo-sensitive member than a belt, for which reason there is a demand to impart even greater flexibility to the developer roller.
The developer roller surface member used in a developing apparatus is continually in contact with the toner, wherefore that member needs to exhibit outstanding toner releasability and wear resistance, while exhibiting little deterioration in properties. Conventionally, a number of materials have been proposed therefor.
In terms of examples wherein materials of outstanding wear resistance are used, many materials have been proposed, such as resins reinforced with the dispersion of carbon fiber therein (Japanese Patent Application Laid-Open No. S61-23171/1986 (published)), examples wherein glass powder is contained in ceramic coating material (Japanese Patent Application Laid-Open No. H4-7568/1992 (published)), certain silica-containing silicone rubbers (Japanese Patent Application Laid-Open No. H9-292768/1997 (published)), and examples wherein the surface is coated with a polyamide (Japanese Patent Application Laid-Open No. H6-149031/1994 (published)).
There are also examples wherein releasability has been improved, such as examples wherein a phenol resin surface coating film containing electroconductive carbon and graphite is formed (Japanese Patent Application Laid-Open No. H3-12676/1991 (published), examples wherein a titanate coupling agent is used (Japanese Patent Application Laid-Open No. H4-19761/1992 (published), examples wherein a fluorine-based surfactant is contained (Japanese Patent Application Laid-Open No. H4-22979/1992 (published)), and examples wherein a solid lubricant is used (Japanese Patent Application Laid-Open No. H8-211726/1996 (published)).
There are, in addition thereto, examples that seek to resolve the problems with both properties such as examples wherein crystalline and amorphous polyamide resins are mixed (Japanese Patent Application Laid-Open No. H4-247478/1992 (published)).
Nevertheless, in the conventional examples noted above, in those where toner releasability is outstanding, there will be surfaces that prevent the adhesion of toner due to the fact that the surface is gradually worn away, wherefore it has been very difficult to realize both releasability and wear properties together.
In order to eliminate the above problem, an object of the present invention is to provide a developing apparatus having excellent toner releasability with respect to a layer thickness regulating member or developer bearing member. More specifically, the present invention provides a developing apparatus wherein developer charging qualities that are stable over time and a uniform thin layer of developer can be obtained, and the generation of reverse charged toner is reduced, and to provide a developing apparatus wherein a uniform stable thin toner layer is obtained even when the developer bearing member is a rigid member.
An embodiment of the present invention provides a developing apparatus having a thin layer roller employed, in which a thin layer roller having elasticity can also be employed and with which toner filming and aggregate adhesion do not occur on the surface of the thin layer roller when used for an extended period, and further provides a developing apparatus with which the toner charging characteristics have been improved and generation of reverse charged toner is reduced.
Another embodiment of the present invention provides a developing unit and image forming apparatus wherein both the toner releasability and wear resistance of the developer roller are satisfactory, and a stable thin toner layer is obtained.
Further, the present invention has an object to provide a high-image-quality, highly durable image forming apparatus.
The first embodiment of the present invention is a developing apparatus for developing a latent electrostatic image to a developed image with a developer, comprising a developer bearing member capable of bearing the developer on a surface portion of the developer bearing member, and a layer thickness regulating member for regulating the thickness of said developer on the developer bearing member to a uniform thickness, the surface portion of the layer thickness regulating member comprising a material which comprises at least one component selected from the group consisting of a cross-linked alkylalkoxyl-group containing nylon resin and a cyclic polyolefin.
The second embodiment of the present invention is a developing apparatus of the first embodiment, wherein the surface portion of said layer thickness regulating member has a volume resistivity of 1012 xcexa9cm or less.
The third embodiment of the present invention is a developing apparatus of the first embodiment, wherein said layer thickness regulating member has an elastic layer.
The fourth embodiment of the present invention is a developing apparatus of the first embodiment, wherein the layer thickness regulating member is a roller.
The fifth embodiment of the present invention is a developing apparatus of the fourth embodiment, wherein the material comprising the cyclic polyolefin and a polyethylene wax.
The sixth embodiment of the present invention is a developing apparatus of the fourth embodiment, wherein the material comprising the cyclic polyolefin, and a compound that is positioned, in triboelectric series, more to positive charge side than the polyolefin.
The seventh embodiment of the present invention is a developing apparatus of the first embodiment, wherein the nylon resin containing crosslinked alkylalcoxyl group is obtained using 30 parts by weight or less of a crosslinking agent to 100 parts by weight of said nylon resin containing alkylalcoxyl group.
The eighth embodiment of the present invention is a developing apparatus of the first embodiment, wherein the nylon resin containing crosslinked alkylalcoxyl group is obtained using a silane coupling agent as crosslinking agent.
The ninth embodiment of the present invention is a developing apparatus of the eighth embodiment, wherein the silane coupling agent is an aminosilane coupling agent.
The tenth embodiment of the present invention is a developing apparatus of the first embodiment, wherein the alkylalcoxyl group is a methylmethoxyl group.
The eleventh embodiment of the present invention is a developing apparatus of the first embodiment, wherein at least the surface of the developer bearing member comprises a material comprising polyimide denatured silicone.
The twelfth embodiment of the present invention is a developing apparatus of the first embodiment, wherein the surface portion of said developer bearing member has a volume resistivity of 1012 xcexa9cm or less.
The thirteenth embodiment of the present invention is a developing apparatus of the first embodiment, wherein the developer bearing member has an elastic layer.
The fourteenth embodiment of the present invention is a developing apparatus of the eleventh embodiment, wherein the material comprises 15 parts by mass or more of at least one of a maleimide resin having a group of quaternary ammonium salt and a methacrylimide resin having a group of quaternary ammonium salt to 100 parts by mass of said polyimide denatured silicone.
The fifteenth embodiment of the present invention is a developing apparatus for supplying developer to latent electrostatic images and making those latent electrostatic images visible to form developed images, comprising a developer bearing member capable of carrying developer on the surface thereof, and a layer thickness regulating member for regulating developer carried on the developer bearing member to a uniform thickness, wherein at least the surface of the developer bearing member is formed of a material comprising mainly of a polyimide denatured silicone.
With the constitution of the present invention as described above, the use of polyimide denatured silicone resin having excellent releasability and abrasion resistance on the surface of the developer roller make it possible to obtain a developing apparatus which causes no toner retention, and provides toner with stable toner electrostatic properties and the thin layer with stable uniformity because of its desirable resistance to abrasion.
The sixteenth embodiment of the present invention is the developing apparatus according to the fifteenth embodiment described above, wherein the surface portion of the developer bearing member has a volume resistivity of 1012 xcexa9cm or less.
The seventeenth embodiment of the present invention is the developing apparatus according to the fifteenth embodiment described above, wherein the developer bearing member has an elastic layer.
The eighteenth embodiment of the present invention is the developing apparatus according to the fifteenth embodiment, wherein the material comprising mainly of polyimide denatured silicone contains 15 parts by mass or more of at least one of a maleimide resin containing a quaternary ammonium salt and a methacrylimide resin containing a quaternary ammonium salt to 100 parts by mass of the polyimide denatured silicone.
With the constitution described above, it is possible to obtain a developing unit which not only can control the resistance uniformly but also control the electrostatic property of the toner on the developer roller at the same time.
The nineteenth embodiment of the present invention is an image forming apparatus comprising a latent electrostatic image bearing means capable of bearing latent electrostatic images thereon, charging means for electrically charging the surface of the latent electrostatic image bearing means, exposing means for exposing the surface of the electrically charged latent electrostatic image bearing means to light imagewise so as to form a latent electrostatic image thereon corresponding to an image to be formed, a developing member comprising a develop unit for supplying the developer to the latent electrostatic image and developing the latent electrostatic image to a developed image with the developer, which developing unit comprises, (a) a developer bearing member capable of bearing the developer on a surface portion of the developer bearing member, and (b) a layer thickness regulating member for regulating the thickness of a layer of the developer on the developer bearing member to a uniform thickness, the surface portion of the layer thickness regulating member comprising a material which comprises at least one component selected from the group consisting of a cross-linked alkylalkoxyl-group-containing nylon resin and a cyclic polyolefin.
The twentieth embodiment of the present invention is an image forming apparatus comprising a latent electrostatic image bearing means capable of bearing latent electrostatic images thereon, charging means for electrically charging the surface of the latent electrostatic image bearing means, exposing means for exposing the surface of the electrically charged latent electrostatic image bearing means to light imagewise so as to form a latent electrostatic image thereon corresponding to an image to be formed, a developing member comprising a develop unit for supplying the developer to the latent electrostatic image and developing the latent electrostatic image to a developed image with the developer, which developing unit comprises,(a) a developer bearing member capable of bearing the developer on a surface portion of the developer bearing member, and (b) a layer thickness regulating member for regulating the thickness of a layer of the developer on the developer bearing member to a uniform thickness, the surface portion of the developer bearing member comprising a material containing a polyimide denatured silicone.
With the constitution described above, it is possible to obtain an image forming apparatus having high image quality and high durability.